1. Field of the Invention
The present invention relates generally to a method and apparatus for decreasing handover latency in heterogeneous networks, and in particular, to a method and apparatus for decreasing a handover latency time using a context exchange between a mobile terminal and a Media Independent Handover Server (MIHS).
2. Description of the Related Art
Handovers are largely classified into a hard handover, a soft handover, and a seamless handover. In particular, a handover between heterogeneous networks (a vertical handover (VHO)) requires a continuous service through the seamless handover and power saving of a mobile terminal.
However, in a conventional VHO method, the execution latency of a VHO is long. Since discontinuity in packet transfer occurs if the VHO execution latency time is long, continuous communications cannot be smoothly accomplished. In addition, according to the conventional VHO method, two modes must be simultaneously monitored. That is, a mobile terminal must periodically wake up in order to receive information regarding a currently unused mode through a downlink. Thus, a dual mode terminal consumes more power than a single mode terminal.
In order to describe the VHO execution latency time, it is assumed that a mobile terminal (MT) has a dual mode of Wireless Local Area Network (WLAN) and Worldwide Interoperability for Microwave Access (WiMAX). In addition, it is assumed that a mobile terminal (MT) is located in an area where the two modes coexist and is currently communicating through WLAN.
If the MT desires to handover to a WiMAX Access Network (AN), the MT pre-sets a WiMAX wireless channel and performs a handover process through the pre-set WiMAX wireless channel. In this case, the MT performs the handover process by securing the WiMAX wireless channel in an early stage. Thus, handover latency is relatively short. However, a time period in which WLAN and WiMAX must operate at the same time is long. That is, since the MT must communicate through WLAN even while performing the handover process to WiMAX, power consumption of the MT is maximized.
According to the prior art, before setting the WiMAX wireless channel, the MT can perform the handover process to WiMAX through a currently used WLAN channel. In this case, the MT pre-performs a portion related to the handover process to WiMAX through the currently activated WLAN channel instead of securing the WiMAX wireless channel in an early stage. That is, the MT uses only one mode during the VHO by performing resource allocation signaling for requesting for resources to be used in a WiMAX area through the WLAN channel. Thus, power consumption is reduced. However, since the MT must perform VHO-related signaling to the WiMAX area, the time required for the VHO is greatly increased.
Thus, a handover latency decreasing method is required, whereby an MT can reduce a VHO execution latency time and consume almost the same power as a single mode terminal.